Many modern computer based devices are equipped with a variety of different types of ports for external devices. Such ports include the USB (Universal Serial Bus) port, the Firewire port, and memory card slots. These types of ports provide a power supply to the device to which they are connected.
In systems that comprise a plurality of ports (sometimes more than six (6) ports) allocating the maximum required current rating for each of the plurality of ports may place a very high power requirement on the power supply unit of the system. Consider, for example, the exemplary prior art system 100 that is illustrated in FIG. 1.
The power supply unit 110 of the system 100 provides power to a power switch 120. The power switch 120 has a current rating of one and one half amperes (1.5 A). That means that the power switch 120 is designed to carry a maximum current of one and one half amperes (1.5 A).
The output of the power switch 120 is connected to an input of Port 1 (designated with reference numeral 130) and to an input of Port 2 (designated with reference 140) and to an input of Port 3 (designated with reference numeral 150). Each of the three ports (130, 140, 150) is connected to a separate USB device (not shown in FIG. 1). The USB standard specifies a minimum current of five hundred milliamperes (500 mA) for each port. A five hundred milliampere (500 mA) current is marginal at best for supporting an external USB hard disk.
In the prior art system 100 the power switch 120 has a current rating that is high enough to handle current for each of the three ports (130, 140, 150). The power switch 120 is designed to carry a maximum current of one and one half amperes (1.5 A). Each of the three ports (130, 140, 150) is also designed to carry a maximum current of one and one half amperes (1.5 A).
In response to control signals (not shown in FIG. 1) the power switch 120 sequentially switches power to each of the three ports (130, 140, 150). There is a problem with this arrangement in that if one of the USB devices that is connected to one of the three ports (130, 140, 150) attempts to draw more current than one and one half ampere (1.5 A), then the power switch 120 turns off. When the power switch 120 turns off it abruptly cuts off the supply of power to all the USB devices that are connected to the three ports (130, 140, 150). The cutoff of power could be disastrous for hard disk devices.
There is another problem with this arrangement if one of the USB devices that is connected to one of the three ports (130, 140, 150) malfunctions and continuously draws a current of one and one half (1.5) amperes. In this case there is no protection action from the power switch 120.
A second approach is illustrated in the exemplary prior art system 200 that is shown in FIG. 2. The power supply unit 110 of the system 200 provides power to three different power switches 210, 220 and 230. The power switches 210, 220 and 230 are connected in parallel as shown in FIG. 2. Each of the three power switches 210, 220 and 230 has a current rating of one and one half amperes (1.5 A). That means that each of the three power switches 210, 220 and 230 is designed to carry a maximum current of one and one half amperes (1.5 A).
The output of the first power switch 210 is connected to an input of Port 1 (designated with reference numeral 130). The output of the second power switch 220 is connected to an input of Port 2 (designated with reference 140). The output of the third power switch is connected to an input of Port 3 (designated with reference numeral 150). Each of the three ports (130, 140, 150) is connected to a separate USB device (not shown in FIG. 2).
In the prior art system 200 the first power switch 210 has a current rating that is high enough to handle current for the first port (Port 1) 130. The first power switch 210 is designed to carry a maximum current of one and one half amperes (1.5 A). The second power switch 220 has a current rating that is high enough to handle current for the second port (Port 2) 140. The third power switch 230 has a current rating that is high enough to handle current for the third port (Port 3) 150. Each of the three ports (130, 140, 150) is also designed to carry a maximum current of one and one half amperes (1.5 A).
Each of the three power switches (210, 220, 230) is connected only to its respective port (130, 140, 150). In this manner the three ports (130, 140, 150) are isolated from each other. In response to control signals (not shown in FIG. 2) each of the three power switches (210, 220, 230) separately provide power to each of the three ports (130, 140, 150).
In the system 200 if one of the USB devices that is connected to one of the ports (e.g., Port 1 130) attempts to draw more current than one and one half ampere (1.5 A), then the first power switch 210 turns off. When the first power switch 210 turns off it abruptly cuts off the supply of power to the USB device that is connected to the first power (130). Power to the other ports is unaffected.
However, the system 200 dose not solve the problem that arises when one of the USB devices that is connected to one of the three ports (130, 140, 150) malfunctions and draws one and one half amperes (1.5 A) of current continuously. In addition, the power supply unit 110 for the system 200 will have an extremely high current requirement (e.g., 4.5 A @5V for three (3) ports).
To remedy the deficiencies of the above identified prior art methods there is a need in the art for an improved apparatus and method for providing power to electronic devices through power switches.